A variety of rock-magnetic measurements was made on sediment
samples from Ceara Rise, Leg 154, Site 925 of the Ocean Drilling
Program. Ceara Rise sediments are composed of marine carbonates
and terrigenous material from the Amazon Fan. Bulk
susceptibility, which measures approximately the concentration of
strongly magnetic particles (e.g., magnetite, maghemite) in the
sediment, can be used as a climate proxy signal that is based on
the dilution of terrigenous material by ocean-derived carbonates.
During interglacial periods, the high-susceptibility terrigenous
material is diluted, resulting in a minimum in susceptibility.
This hypothesis is supported by the inverse correlation between
the smoothed susceptibility record and the 
low latitude record. Anhysteretic
remanent magnetization (ARM), contributed primarily by magnetic
grains from 0.1 to 15 µm, was normalized by susceptibility (c),
giving a parameter that is sensitive to magnetic grain size.
Variations of ARM/c show high values during interglacials and low
values during glacials. The source of this material is most
likely from an increase of Amazon Basin soil runoff during
interglacial periods.
1Shackleton, N.J., Curry, W.B., Richter, C., and Bralower, T.J. (Eds.), 1997. Proc. ODP, Sci. Results, 154: College Station, TX (Ocean Drilling Program).
2Institute for Rock Magnetism, University of Minnesota, Minneapolis MN 55455-0128, U.S.A. peat@tc.umn.edu.
3Ocean Drilling Program, 1000 Discovery Drive, Texas A&M University, College Station, TX 77845-4857, U.S.A.
4Institut de Physique du Globe, 4 Place Jussieu, 75252 Paris Cedex 05, France.
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